It probably depends on what you're trying to do; I needed Markdown styling and Markdown-aware behaviors (e.g. when you hit return after a list item, indent the same amount and add a new list marker), context-aware nesting (hit Command-[/] to indent/outdent), hotkeys for heading levels, and so on. Between keeping the attributed text styles correct, properly grabbing the right text ranges to operate on, and doing it all in undoable transactions, it became a handful.